Living Carbocationic Polymerization of Isobutylene Using Blocked Dicumyl Chloride or Tricumyl Chloride/TiCI4Pyridine Initiating System

Abstract

Living polymerization of isobutylene was achieved using an initiation system based on either 1,3-di(1-chloro-l-methylethyl)-5-tert-butylbenzene (tert-butyl-dicumyl chloride) or 1,3,5-tris(l-chloro-l-methylethyl)benzene (tricumyl chloride) in conjunction with TiCl₄, and pyridine in hexanes/methyl chloride (60/40, v/v) cosolvents. TiCl₄/pyridine was found to yield narrow molecular weight distribution (MWD ≈ 1.1) and quantitative initiation efficiency (I_eff < 90%). The living nature of the polymerization system was demonstrated by the linearity of molecular weight vs conversion plots and first-order kinetic plots up to about 90% monomer conversion. If polymerization was allowed to proceed further, a departure from first-order kinetics and a broadening of the molecular weight distribution was observed to occur. The living polymerization was investigated as a function of temperature, reaction time, and the concentration of TiCl₄/pyridine. Polymerization rates were observed to increase with decreasing temperature and/or increasing concentration of TiCl₄/pyridine. Number-average molecular weights of the polyisobutylenes ranged from 5,000 to 100,000 under the conditions employed.     

Novel Epoxide Initiators for the Carbocationic Polymerization of Isobutylene

Summary: We recently reported the synthesis of polyisobutylene (PIB) via direct initiation by epoxycyclohexyl isobutyl polyhedral oligomeric silsesquioxane (POSS®) (Figure 1 ) in conjunction with titanium tetrachloride (TiCl₄). This system successfully initiated the living carbocationic polymerization of isobutylene (IB) in hexane/methyl chloride (Hx/MeCl -60/40, v/v) at T = −80 °C, yielding an asymmetric telechelic PIB with one POSS® cage head group and one tert-Cl end group. 1 This paper will discuss IB polymerizations initiated by 1,2-epoxycyclohexane and bis[3,4-(epoxycyclohexyl)ethyl]-tetramethyl-disiloxane, in conjunction with TiCl₄.     

Polyisobutylene-containing block polymers by sequential monomer addition. I. The living carbocationic polymerization of styrene

The living carbocationic polymerisation of styrene (St) has been investigated by the 2-chloro-2,4,4-trimethylpentane (TMPCI)/TiCl₄ initiating system in the presence of various additives such as electron pair donors (ED_s) and the proton trap 2,6-di-tert-butylpyridine (DtBP) by the use of the mixed solvent CH₃Cl/methyl-cyclohexane (MCHx) (40/60 v/v) at ?80°C under conventional laboratory conditions. The TMPCl/TiCl₄ system in the absence of additives produces ill-defined bimodal molecular weight distribution (MWD) polymers. Much better defined polystyrenes (PSt) can be obtained in the presence of EDs, such as N,N-dimethylacetamide (DMA) and hexamethylphosphoramide (HMPA). Monomer depletion should be avoided to prevent intra- or intermolecular alkylation yielding indanyl end groups or branched polymers, respectively. In the combined presence of an ED and the proton trap, i.e., DMA + DtBP, the living polymerization of St has been achieved and thus the foundations for the carbocationic synthesis of PSt block polymers by sequential monomer addition have been laid.     

Living Carbocationic Polymerization of p-Methylstyrene and Sequential Block Copolymerization of Isobutylene with p-Methylstyrene

Abstract

A novel scheme was developed for the synthesis of pure polyisobutylene-poly(p-methylstyrene) block copolymers by sequential monomer addition. The synthesis involves the living polymerization of isobutylene by the TiCl₄/methyl chloride:methylcyclohexane or hexanes 40:60 v:v/ -80°C system in the presence of di-tert-butylpyridine. When the polymerization of isobutylene is complete, the living polyisobutylene chain end is transformed to the corresponding diphenyl alkyl end by capping with 1,1-diphenylethylene. Subsequently, titanium(IV) isopropoxide or titanium(IV) butoxide is added to decrease the Lewis acidity followed by the addition of p-methylstyrene. The success of the method was demonstrated by p-methylstyrene homopolymerization experiments initiated by 2-chloro-2,4,4-trimethylpentane that resulted in ～ 100% initiator efficiencies when the TiCl₄/titanium(IV) isopropoxide or -butoxide ratio was less than 25/7, as well as by the clean synthesis of polyisobutylenepoly(p-methylstyrene) diblock copolymers.     

Comparison of the Mechanism and Kinetics of Living Carbocationic Isobutylene and Styrene Polymerizations Based on Real-Time FTIR Monitoring

This paper will compare the mechanism and kinetics of living carbocationic polymerization of isobutylene (IB) and styrene (St), initiated by the 2-chloro-2,4,4-trimethyl-pentane (TMPCl) / TiCl₄) system in 60/40 (v/v) methylcyclohexane / methyl chloride mixed solvent at −80 and −75 °C. The rate of initiation was found to be first order in TiCl₄ in both systems. While initiation is instantaneous in IB polymerization at [TiCl₄]₀ ⩾ [TMPCl]₀, it is slow in St polymerization. Kinetic derivation showed that initiating efficiency is dependent on [M] in this latter system, which was also demonstrated experimentally. The apparent initiation rate constant was determined from initiator consumption rate data and was found to be k_i,app = 1.39 l²/mol²sec. The rate of St consumption measured using a real time fibre-optic mid-FTIR monitoring technique compared well with gravimetric data and was found to be closer to first order in TiCl₄ at [TiCl₄]₀ < [TMPCl]₀. However, the rate followed a close to second order in TiCl₄ at [TiCl₄]₀ ⩾ [TMPCl]₀. The mechanistic model proposed earlier for living carbocationic IB polymerization, which yielded good agreement with experimental data, seems to apply to carbocationic St polymerization as well. This model reconciles the discrepancy between rate constants published for carbocationic IB and St polymerizations, and accounts for shifting TiCl₄ orders. However, independent investigations are necessary to verify the proposed mechanistic model. Optimized conditions led to living carbocationic St polymerization producing high molecular weight PS with 100% initiating efficiency.     

The role of pyridine derivatives in living carbocationic polymerization: Lewis base or nucleophile?

The living cationic polymerization of isobutylene induced by the 2-chloro-2,4,4-trimethylpentane/TiCl₄/hexane:methyl chloride (60:40, v:v)/-80°C system was studied in the presence of pyridine derivatives. Protic initiation, substantial in the absence of these additives, was virtually eliminated in their presence, and polyisobutylenes with controlled molecular weight and narrow molecular weight distribution were obtained. With some additives, however, proton elimination occurs, resulting in the exclusive formation of the exo olefin. The rate of elimination is independent of monomer concentration, i.e., it occurs during and after the polymerization. Results suggest that the proton elimination is due to the presence of an uncomplexed base, especially when complex formation with TiCl₄ is hindered by steric compression, but its approach of the polymer cation is not fully blocked.     

Kinetic study of the living cationic polymerization of isobutylene using t-Bu-m-DCC/TICL4/2,4-dimethylpyridine initiating system

Kinetics of the living cationic polymerization of isobutylene, initiated by the system t-bu-m-DCC/TiCl₄/2,4-dimethylpyridine (2,4-DMP), were studied as a function of concentration of the various components of the initiation system, solvent polarity, and presence of the protic acid scavenger, 2,6-di-tert-butylpyridine (DTBP). Under a variety of conditions, the effective number of growing chains in a given polymerization remained constant and Mn increased linearly with monomer conversion. The system was found to yield an essentially homogeneous reaction mixture in hexanes/methyl chloride cosolvents, with only a small amount of precipitate, probably 2,4-dimethylpyridinium salts resulting from proton scavenging by the tertiary amine. It was found that increasing [TiCl₄] strongly increased the rate while increasing [2,4-DMP] weakly decreased the rate. Evidence of a retardation of the polymerization rate by the soluble TiCl₄:2,4-DMP complex was observed. The addition of DTBP as a protic acid scavenger, with or without 2,4-DMP, very weakly decreased the rate of polymerization. Increasing the fraction of methyl chloride in the solvent mixture caused an increase in the rate of polymerization. All of the results were consistent with a propagation mechanism in which an equilibrium exists between dormant and ionized, active chain ends.     

Living Carbocationic Polymerization. XLIX. Two-Stage Living Polymerization of Isobutylene to Di-tert-chlorine Telechelic Polyisobutylene

Abstract

A two-stage process was developed for the living polymerization of isobutylene (IB) employing di-tert-alcohol initiators in conjunction with BCl₃ coinitiator in the first or initiation stage, followed by TiCl₄ coinitiator in the second or propagation stage; the process was shown to yield high molecular weight (up to M ⁿ 20,000), narrow molecular weight distribution (MWD) M ^w/M ⁿ = 1.1–1.2) di-tert-chlorine telechelic polyisobutylenes (^tCl-PIB-Cl^t). The initiation stage involves the homogeneous solution living polymerization of IB induced by the di-tert-alcohol/BCl₃ combination in the presence of an electron donor such as N,N-dimethylacetamide in CH₃Cl solvent at ?80°C and proceeds up to M ⁿ < 5000; this is followed by the propagation stage in which TiCl₄ and the bulk of IB plus a sufficient amount of n-C₆H₁₄ are added to the charge to bring the solvent composition to CH₃Cl/n-C₆H₁₄ 60/40 v/v and the living polymerization is continued until high M ⁿ product is obtained. This two-stage process was developed because 1) it employs very inexpensive chemicals; 2) di-tert-alcohol/BCl₃ combinations initiate living IB polymerization in CH₃Cl but the product after reaching M ⁿ ≤ 5000 precipitates out of the CH₃Cl solution, and di-tert-alcohol/BCl₄ combinations do not initiate IB polymerization; and 3) di-tert-alcohol/BCl₃ systems do not initiate (or only very slowly) the living polymerization of IB in CH₃Cl/n-C₆H₁₄ mixtures, whereas similar TiCl₄-based systems do. The polymerization remains living during both stages although the propagating species and solvent polarity are profoundly altered. The livingness of the system has been analyzed by kinetic experiments and the structure of the ^tCl-PIB-Cl^t product by routine spectroscopic means.     

Synthesis of polyisobutylene with arylamino terminal group by combination of cationic polymerization with alkylation

The controlled cationic polymerization of isobutylene (IB) initiated by H₂O as initiator and TiCl₄ as coinitiator was carried out in n‐Hexane/CH₂Cl₂ (60/40, v/v) mixture at −40 °C in the presence of N,N‐dimethylacetamide (DMA). Polyisobutylene (PIB) with nearly theoretical molecular weight (M_n = 1.0 × 10⁴ g/mol), polydispersity (M_w/M_n) of 1.5 and high content (87.3%) of reactive end groups (tert‐Chlorine and α‐double bond) was obtained. The Friedel‐Crafts alkylation of triphenylamine (TPA) with the above reactive PIB was further conducted at different reactions, such as [TPA]/[PIB], solvent polarity, alkylation temperature, and time. The resultant PIBs with arylamino terminal group were characterized by ¹H NMR, UV, and GPC with RI/UV dual detectors. The experimental results indicate that alkylation efficiency (A_eff) increased with increases in [TPA]/[PIB], reaction temperature, and reaction time and with a decrease in solvent polarity. The alkylation efficiency could reach 81.0% at 60/40(v/v) mixture of n‐Hex/CH₂Cl₂ with [TPA]/[PIB] of 4.49 at 50 °C for 54 h. Interestingly, the synthesis of PIB with arylamino terminal group could also be achieved in one pot by combination of the cationic polymerization of IB initiated by H₂O/TiCl₄/DMA system with the successive alkylation by further introduction of TPA. Mono‐, di‐ or tri‐alkylation occurred experimentally with different molar ratio of [TPA]/[PIB]. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 936–946, 2008     

Living Carbocationic Polymerization. LVII. Kinetic Treatment of Living Carbocationic Polymerization Mediated by the Common Ion Effect

Abstract

The effect of anion concentration on the apparent rate constant of polymerization k^A _p of isobutylene (IB) induced by the 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl₄ initiating system using the CH₂Cl₂/nC₆H₁₄ (60/40 v/v) solvent system at ?40 and ?80°C was studied by the use of nBu₄NCl. Computer simulation has shown that k^A _p decreases several orders of magnitude upon the addition of even a very small amount of common anion TiCl^?- ₅ to the charge. The rate of change is reduced in the concentration range of experimental interest. It was concluded that the decrease of k^A _p with increasing TiCl ^?- ₅ concentration is mainly due to the decreasing contribution of propagation by free ions. The contribution (%) of propagation by free ions to the apparent rate of propagation was calculated.     

Living carbocationic copolymerization of isobutylene with styrene

The carbocationic copolymerization of isobutylene (IB) and styrene (St), initiated by 2‐chloro‐2,4,4‐trimethylpentane/TiCl₄ in 60/40 (v/v) methyl chloride/hexane at ?90 °C, was investigated. At a low total concentration (0.5 mol/L), slow initiation and rapid monomer conversion were observed. At a high total comonomer concentration (3 mol/L), living conditions (a linear semilogarithmic rate and M_n–conversion plots) were found, provided that the St concentration was above a critical value ([St]₀ ～ 0.6 mol/L). The breadth of the molecular weight distribution decreased with increasing IB concentration in the feed, reaching M_w/M_n ～ 1.1. St homopolymerization was also living at a high total concentration, yielding polystyrene with M_n = 82,000 g/mol, the highest molecular weight ever achieved in carbocationic St polymerization. An analysis of this system by both the traditional gravimetric–NMR copolymer composition method and FTIR demonstrated penultimate effects. IB enrichment was found in the copolymers at all feed compositions, with very little drift at a high total concentration and above the critical St concentration. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1778–1787, 2007     

Living Cationic Sequential Block Copolymerization of Isobutylene with 4‐tert‐Butoxystyrene: Synthesis and Characterization of Poly(p‐hydroxystyrene‐b‐isobutylene‐b‐p‐hydroxystyrene) Triblock Copolymers

The living polymerization of p‐tert‐butoxystyrene (tBuOS) was studied in methylcyclohexane (MeChx)/methylchloride (MeCl) 60/40 v/v solvent mixture at –80°C. The model initiator 1,1,‐ditolylethylene (DTE) capped 2‐chloro‐2,4,4‐trimethylpentane (TMPCl) was formed in situ in conjunction with TiCl₄. Lowering the Lewis acidity by the addition of Ti(OIp)₄ was necessary to induce a rapid and controlled polymerization of tBuOS. Well‐defined polymers with controlled molecular weights, however, were only obtained at a narrow [Ti(OIp)₄]/[TiCl₄]=0.83–0.86 ratio. Above this ratio, the polymerization of tBuOS was slow and became absent at [Ti(OIp)₄]/[TiCl₄]≥1.18. At ratios lower than 0.83, the polymerization was too rapid and the initiator efficiency was lower than 100%. The living polymerization of tBuOS was also studied with SnBr₄ as Lewis acid. After capping TMPCl with DTE, Ti(OIp)₄ was added to reach [Ti(OIp)₄]/[TiCl₄]=1.2, followed by the addition of tBuOS and SnBr₄. SnBr₄ induced a well‐controlled living polymerization approximately first order in [SnBr₄], and the polymers exhibited close to theoretical M _ns and low polydispersity indices (PDI<1.2). The success of the method was also demonstrated by the clean synthesis of poly(isobutylene‐b‐p‐tert‐butoxystyrene) PIB‐b‐PtBuOS diblock copolymers. PtBuOS‐b‐PIB‐b‐PtBuOS triblock copolymer thermoplastic elastomers were prepared by employing 5‐tert‐butyl‐1,3‐bis(1‐methoxy‐1‐methylethyl)benzene (DCE) as a difunctional initiator for the living polymerization of IB followed by capping with DTE and substitution of TiCl₄ with SnBr₄ for the polymerization of tBuOS. Deprotection of the triblock copolymer in the presence of catalytic amount of HCl yielded poly(p‐hydroxystyrene‐b‐isobutylene‐b‐p‐hydroxystyrene) (PHOS‐b‐PIB‐b‐PHOS). PHOS‐b‐PIB‐b‐PHOS with 39.3 wt% p‐hydroxystyrene content exhibited typical characteristic of a thermoplastic elastomers (TPEs) with tensile strength of 18 MPa and ultimate elongation of 300%.     

Polyisobutylene-Based Thermoplastic Elastomers. I. Synthesis and Characterization of Polystyrene-Polyisobutylene-Polystyrene Triblock Copolymers

Abstract

Polystyrene-polyisobutylene-polystyrene triblock copolymer thermoplastic elastomers have been synthesized by living carbocationic sequential copolymerization using the tert-butyl dicumyl chloride/TiCl₄/methylcyclohexane:methyl chloride (60:40 v:v)/ ?80°C system in the presence of the proton trap 2,6-di-tert-butylpyridine. Structure-property relationships have been examined by varying the M_n of the PIB middle block (39,000 to 156,000) and that of the PSt end-segment (1,000 to 19,000). The tensile strength is controlled by the molecular weight of the PSt segment and independent of the PIB middle block length in the studied range. Phase separation starts when the M_n of the PSt segment reaches ～ 5,000, and it is complete when the M_n reaches ～ 15,000. These triblocks exhibited 23-25 MPa tensile strength, similar to that of styrenic thermoplastic elastomers obtained by anionic polymerization.     

Synthesis of 1-chloro-1-phenylethyl-telechelic polyisobutylene,a new potential macroinitiator by living cationic polymerization

1-Chloro-1-phenylethyl-telechelic polyisobutylene (PIB) was synthesized by living carbocationic polymerization (LCCP). LCCP of isobutylene was induced by a difunctional initiator in conjunction with TiCl₄ as coinitiator in the presence of N,N-dimethylacetamide in CH₂Cl₂/hexane (40:60 v/v) solvent mixture at −78°C. After complete isobutylene conversion a small amount of styrene was added leading to a rapid crossover reaction and thus to the attachment of short outer polystyrene (PSt) blocks to the PIB segment. Quenching the living polymerization of styrene yielded 1-chloro-1-phenylethyl terminal groups. The resulting telechelic polymer (Cl-PSt-PIB-PSt-Cl) is a potential new macroinitiator for atom transfer radical polymerization of a variety of vinyl monomers.     

Living cationic polymerization of vinyl ethers in the presence of a strong base: Poisonous or helpful?

A quite small dose of a poisonous species was found to induce living cationic polymerization of isobutyl vinyl ether (IBVE) in toluene at 0 °C. In the presence of a small amount of N,N‐dimethylacetamide, living cationic polymerization of IBVE was achieved using SnCl₄, producing a low polydispersity polymer (weight–average molecular weight/number–average molecular weight (M_w/M_n) ≤ 1.1), whereas the polymerization was terminated at its higher concentration. In addition, amine derivatives (common terminators) as stronger bases allow living polymerization when a catalytic quantity was used. On the other hand, EtAlCl₂ produced polymers with comparatively broad MWDs (M_w/M_n ～ 2), although the polymerization was slightly retarded. The systems with a strong base required much less quantity of bases than weak base systems such as ethers or esters for living polymerization. The strong base system exhibited Lewis acid preference: living polymerization proceeded only with SnCl₄, TiCl₄, or ZnCl₂, whereas a range of Lewis acids are effective for achieving living polymerization in the conventional weak base system such as an ester and an ether. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6746–6753, 2008     

Poly(styrene‐b‐isobutylene) multiarm star‐block copolymers

Multiarm star‐branched polymers based on poly(styrene‐b‐isobutylene) (PS‐PIB) block copolymer arms were synthesized under controlled/living cationic polymerization conditions using the 2‐chloro‐2‐propylbenzene (CCl)/TiCl₄/pyridine (Py) initiating system and divinylbenzene (DVB) as gel‐core‐forming comonomer. To optimize the timing of isobutylene (IB) addition to living PS⊕, the kinetics of styrene (St) polymerization at −80°C were measured in both 60 : 40 (v : v) methyl cyclohexane (MCHx) : MeCl and 60 : 40 hexane : MeCl cosolvents. For either cosolvent system, it was found that the polymerizations followed first‐order kinetics with respect to the monomer and the number of actively growing chains remained invariant. The rate of polymerization was slower in MCHx : MeCl (k_app = 2.5 × 10⁻³ s⁻¹) compared with hexane : MeCl (k_app = 5.6 × 10⁻³ s⁻¹) ([CCl]_o = [TiCl₄]/15 = 3.64 × 10⁻³M; [Py] = 4 × 10⁻³M; [St]_o = 0.35M). Intermolecular alkylation reactions were observed at [St]_o = 0.93M but could be suppressed by avoiding very high St conversion and by setting [St]_o ≤ 0.35M. For St polymerization, k_app = 1.1 × 10⁻³ s⁻¹ ([CCl]_o = [TiCl₄]/15 = 1.82 × 10⁻³M; [Py] = 4 × 10⁻³M; [St]_o = 0.35M); this was significantly higher than that observed for IB polymerization (k_app = 3.0 × 10⁻⁴ s⁻¹; [CCl]_o = [Py] = [TiCl₄]/15 = 1.86 × 10⁻³M; [IB]_o = 1.0M). Blocking efficiencies were higher in hexane : MeCl compared with MCHx : MeCl cosolvent system. Star formation was faster with PS‐PIB arms compared with PIB homopolymer arms under similar conditions. Using [DVB] = 5.6 × 10⁻²M = 10 times chain end concentration, 92% of PS‐PIB arms (M_n,PS = 2600 and M_n,PIB = 13,400 g/mol) were linked within 1 h at −80°C with negligible star–star coupling. It was difficult to achieve complete linking of all the arms prior to the onset of star–star coupling. Apparently, the presence of the St block allows the PS‐PIB block copolymer arms to be incorporated into growing star polymers by an additional mechanism, namely, electrophilic aromatic substitution (EAS), which leads to increased rates of star formation and greater tendency toward star–star coupling. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1629–1641, 1999     

Cationic polymerization of isobutylene with H2O/TiCl4 initiating system in the presence of electron pair donors

Cationic polymerization of isobutylene (IB) in a mixture of methylene dichloride (CH₂Cl₂) and n-hexane (n-Hex) was conducted by using H₂O as initiator, TiCl₄ as co-initiator in the presence of strong external electron pair donor (ED), such as pyridine (Py), dimethylacetamide (DMA) or triethylamine (TEA). The effects of ED concentration, TiCl₄ concentration, solvent polarity, polymerization temperature (T) and time on IB polymerization, molecular weight (MW) and molecular weight distribution (MWD, M_w/M_n) of polyisobutylene (PIB) products were investigated. The relative amount of polymer formed via uncontrolled initiation by conventional active species (I) decreased with increasing the solvent polarity, TiCl₄ concentration and ED concentration in the polymerization. The desirable polymerization of IB with apparent absence of chain transfer reactions could be obtained by H₂O/TiCl₄ initiating system in the presence of ED under the appropriate reaction conditions. The external electron pair donors and TiCl₄ did specially play important and effective roles on polymerization.     

Living carbocationic polymerization of isobutyl vinyl ether and the synthesis of poly[isobutylene-b-(isobutyl vinyl ether)]

The MeCH(O-i-Bu)Cl/TiCl₄/MeCONMe₂ initiating system was found to induce the rapid living carbocationic polymerization (LC^⊕Pzn) of isobutyl vinyl ether (IBuVE) at ?100°C. Degradation by dealcoholation which usually accompanies the polymerization of alkyl vinyl ethers by strong Lewis acids is “frozen out” at this low temperature and poly(isobutyl vinyl ether)s (PIBuVEs) with theoretical molecular weights up to ca. 40,000 g/mol (calculated from the initiator/monomer input) and narrow molecular weight distributions (M?_w/M?_n ≤ 1.2) are readily obtained. According to ¹³C-NMR spectroscopy, PIBuVEs prepared by living polymerization at ?100°C are not stereoregular. The MeCH(O-i-Bu)Cl/TiCl₄ combination induces the rapid LC^⊕Pzn of IBuVE even in the absence of N,N-dimethylacetamide (DMA). The addition of the common ion salt, n-Bu₄NCl to the latter system retards the polymerization and meaningful kinetic information can be obtained. The kinetic findings have been explained in terms of TiCl₄. IBuVE and TiCl₄ · IBuVE and TiCl₄ · PIBuVE complexes. The HCl (formal initiator)/TiCl₄/DMA combination is the first initiating system that can be regarded to induce the LC^⊕Pzn of both isobutylene (IB) and IBuVE. Polyisobutylene (PIB)–PIBuVE diblocks were prepared by sequential monomer addition in “one pot” by the 2-chloro-2,4,4-trimethylpentane (TMP-Cl)/TiCl₄/DMA initiating system. Crossover efficiencies are, however, below 35% because the PIB^⊕ + IBuVE → PIB-b-PIBuVE^⊕ crossover is slow. © 1993 John Wiley & Sons, Inc.     

Polymerization of Methyl Methacrylate with Bis(Cyclopentadienyl)Titanium Dichloride in a Water-Methanol Mixture: Formation of Tetrahydrofuran-Insoluble Polymer

Abstract

Methyl methacrylate (MMA) was found to be effectively polymerized with bis(cyclopentadienyl)titanium dichloride (CP₂TiCl₂) in a water-methanol mixture (1:1, v/v). The polymerization proceeded heterogeneously because the resulting poly(MMA) was insoluble in the system. The rate (R _p) of the heterogenous polymerization was apparently expressed by R _p = k[Cp₂TiCl₂]²[MMA]^2˙5 (at 40°C). The resulting poly(MMA) was observed to consist of tetrahydrofuran (THF)-soluble and insoluble parts. In contrast with the usual radical poly(MMA), the THF-insoluble part was soluble in benzene, toluene, and chloroform but insoluble in polar solvents such as ethyl acetate, acetone, acetonitrile, dimethylformamide, and dimethylsulfoxide. The polymerization was found to be profoundly accelerated by irradiation with a fluorescent room lamp (15 W). The results of copolymerization of MMA and acrylonitrile indicated that the present polymerization proceeds through a radical mechanism.     

Kinetic study on the living/controlled cationic polymerization of p‐methoxystyrene coinitiated by tris(pentafluorophenyl)borane

A kinetic study of the living cationic polymerization of p‐methoxystyrene using 1‐(4‐methoxyphenyl)ethanol ( 1 )/B(C₆F₅)₃ initiating system in a mixture of CH₃CN with CH₂Cl₂ 1:1 (v/v) at room temperature was carried out utilizing a wide variety of conditions. The polymerization proceeded in a living fashion even in the presence of a large amount of water ([H₂O]/[B(C₆F₅)₃] ratio up to 20) to afford polymers whose M_n increased in direct proportion to monomer conversion with fairly narrow MWDs (M_w/M_n ≤ 1.3). The investigation revealed that the rate of polymerization was first‐order in B(C₆F₅)₃ concentration, while a negative order in H₂O concentration close to ?2 was obtained. It was also found that the rate of polymerization decreased with lowering temperature, which could be attributed to a decreased concentration in free Lewis acid, the true coinitiator of polymerization. A mechanistic scheme to explain the kinetic behavior of living p‐methoxystyrene polymerization is proposed, which has been validated by PREDICI simulation on multiple‐data curves obtained by ¹H NMR in situ polymerization experiment. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6928–6939, 2008